--- serf-1.3.2.org/buckets/bwtp_buckets.c
+++ serf-1.3.2/buckets/bwtp_buckets.c
@@ -228,7 +228,7 @@
     req_len = apr_snprintf(ctx->req_line, sizeof(ctx->req_line),
                            "%s %d " "%" APR_UINT64_T_HEX_FMT " %s%s\r\n",
                            (ctx->type ? "BWM" : "BWH"),
-                           ctx->channel, calc_header_size(ctx->headers),
+                           ctx->channel, (long long) calc_header_size(ctx->headers),
                            (ctx->open ? "OPEN " : ""),
                            ctx->phrase);
     new_bucket = serf_bucket_simple_copy_create(ctx->req_line, req_len,
